I have a microcontroller-based widget connected to my home network that monitors some sensors and controls the garage door. I'd like for it to work one way if I'm home and a different way if I'm not home. It could determine if I'm home by looking for my cell phone on the local network. Is there a simple way to do this? The prefered senario is to find the phone at any IP address (using MAC ID?), but I could have the router assign it a fixed IP. Also, it would be better if I didn't have to run an app on the phone, since that will require Android programming and battery drain.